The DAIDS Immunology Quality Assessment Program (IQA) will continue to design and execute proficiency testing programs that periodically assess the ability of laboratories to perform tests correctly, and to provide assistance and training when laboratories have difficulties associated with the HIV/AIDS clinical trial units. Also, the IQA will continue to be a flexible, responsive resource to facilitate the adaptation, standardization and quality assessment of new immunological assay methodologies used in therapeutic, vaccine, prevention, epidemiological and preclinical NIAID investigations. Knowing the broad range of factors affecting assay variability, statisticians are able to determine the appropriate study sample size and design appropriate statistical analysis plans. This, in turn, allows investigators to know if a change in test results is due to an intervention or to inherent assay variability.